In December of 2011, the EPA issued the final Mercury and Air Toxics Standards (MATS) for power plants. MATS requires significant reduction in mercury emissions.
Some mercury can be removed from coal-fired power plant flue gas by SO2 control devices. However, flue gases from coal-fired plants normally comprise significant quantities of elemental mercury and oxidized mercury; and SO2 control devices are suitable for removing oxidized mercury, but not elemental mercury. Low levels of bromine, or aqueous solutions of alkali or alkali-earth metal salts of bromine, such as calcium bromide or sodium bromide, can be used to oxidize the elemental mercury in flue gases. However, when the bromide is oxidized, it results in the formation of bromine. At least some of the bromine can interact with elemental mercury to form mercury salts, such as HgBr2. The excess of bromide value relative to the amount of Hg to be removed results in a significant amount of bromine remaining in the flue gas, which is known to be corrosive to scrubber systems and other equipment in the plant.
Given the foregoing, it would be commercially beneficial to have methods for minimizing mercury emissions from coal-fired power plant flue gases that are suitable for removing both oxidized and elemental mercury from the flue gases without causing corrosion in the plant.